The present invention relates generally to micro-electromechanical (MEM) drop-on-demand liquid emission devices such as, for example, ink jet printers, and more particularly such devices which employ an electrostatic actuator for driving liquid from the device.
Drop-on-demand liquid emission devices with electrostatic actuators are known for ink printing systems. U.S. Pat. Nos. 5,644,341 and 5,668,579, which issued to Fujii et al. on Jul. 1, 1997 and Sep. 16, 1997, respectively, disclose such devices having electrostatic actuators composed of a single diaphragm and opposed electrode. The diaphragm is distorted by application of a first voltage to the electrode. Relaxation of the diaphragm expels an ink droplet from the device. Other devices that operate on the principle of electrostatic attraction are disclosed in U.S. Pat. Nos. 5,739,831, 6,127,198, and 6,318,841; and in U.S. Pub. No. 2001/0023523.
U.S. Pat. No. 6,345,884, teaches a device having an electrostatically deformable membrane with an ink refill hole in the membrane. An electric field applied across the ink deflects the membrane and expels an ink drop.
IEEE Conference Proceeding xe2x80x9cMEMS 1998,xe2x80x9d held Jan. 25-29, 2002 in Heidelberg, Germany, entitled xe2x80x9cA Low Power, Small, Electrostatically-Driven Commercial Inkjet Headxe2x80x9d by S. Darmisuki, et al., discloses a head made by anodically bonding three substrates, two of glass and one of silicon, to form an ink ejector. Drops from an ink cavity are expelled through an orifice in the top glass plate when a membrane formed in the silicon substrate is first pulled down to contact a conductor on the lower glass plate and subsequently released. There is no electric field in the ink. The device occupies a large area and is expensive to manufacture.
U.S. Pat. No. 6,357,865 by J. Kubby et al. teaches a surface micro-machined drop ejector made with deposited polysilicon layers. Drops from an ink cavity are expelled through an orifice in an upper polysilicon layer when a lower polysilicon layer is first pulled down to contact a conductor and is subsequently released.
One such device is disclosed in co-pending U.S. patent application Ser. No. 10/153,990 filed in the names of Gilbert A. Hawkins, et al on May 23, 2002. That device includes an electrostatic drop ejection mechanism that employs an electric field for driving liquid from a chamber in the device. Structurally coupled, separately addressable first and second dual electrodes are movable in a first direction to draw liquid into the chamber and in a second direction to emit a liquid drop from the chamber. A third electrode between the dual electrodes has opposed surfaces respectively facing each of said first and second electrodes at an angle of contact whereby movement of the dual electrodes in one of the first and second directions progressively increases contact between the first and third electrodes, and movement of the dual electrodes in the direction progressively increases contact between the second and third electrodes.
The device described in the Hawkins et al. patent application, and other multi-layer microelectromechanical electrostatic actuators for liquid emission devices, can be manufactured by chemical mechanical polishing in combination with a sacrificial layer to produce a member, having planar surface and a non-planar surface, that can move within a trench left when the sacrificial layer is removed to provide a separation from stationary parts.
According to a feature of the present invention, a drop-on-demand liquid emission device, such as for example an ink jet printer, includes an electrostatic drop ejection mechanism that employs an electric field for driving liquid from a chamber in the device. Structurally coupled, separately addressable first and second dual electrodes are movable in a first direction to draw liquid into the chamber and in a second direction to emit a liquid drop from the chamber. A third electrode between the dual electrodes has opposed surfaces respectively facing each of said first and second electrodes at an angle of contact whereby movement of the dual electrodes in one of the first and second directions progressively increases contact between the first and third electrodes, and movement of the dual electrodes in the direction progressively increases contact between the second and third electrodes.